Metal parts may be produced using "cold chamber" and "hot chamber" die casting apparatuses. Cold chamber apparatuses employ a molten metal reservoir that is separated from the casting machine. Enough metal for one just casting is normally ladled by hand through a port of a small chamber referred to as a shot sleeve. Since this is done by hand it undesirably results in variation in the quantity of molten metal that is fed into the shot sleeve. A hydraulically actuated ram moves in the shot sleeve to force the molten metal under pressure into a die. As the ram advances, it seals the port and forces the charge into the die at pressures which may range from several psi to 60,000 psi or more. The molten metal cools in the chamber prior to injection into the die, thereby lending itself to description as a "cold chamber" process.
The hot chamber process is used for low melting point alloys such as zinc alloys and, may employ, for example, a machine comprising a fixed cylinder having a spout firmly connected to a nozzle locked against a die cavity. A piston operating in the cylinder is raised to uncover an inlet port below the molten metal level in the pot. After the molten metal fills the interior of the cylinder, the piston is forced downward, which causes the molten metal to flow through the spout and into the die. Once the metal solidifies in the die the piston is withdrawn, the die is opened and the casting is removed. The die is then closed and the process repeated.
It is generally believed that better metallurgical castings result from use of the hot chamber process since the molten metal is not cooled as in the cold chamber process. However, numerous attempts have been made to develop a hot chamber apparatus for casting high melting point aluminum without widespread success. In view of difficulties presented in the hot chamber process, the industry could benefit from a cold chamber die casting apparatus which eliminates the risk of workers having to carry out the dangerous task of ladling molten metal, and from a process which produces an accurate charge of molten metal into the shot sleeve.